If the batteries are of the same type, i.e. both are NiMH or both are Lithium-ion, then you can use a higher capacity (i.e. higher mAh) battery instead of the lower one. The reverse is also true.
People visiting Table Rock are not allowed beyond the Mill Creek Watershed boundary, which is clearly marked with numerous signs. As mentioned earlier, the Mill Creek Watershed is a closed watershed and no public access is allowed, as it is the municipal water source for the city of Walla Walla, Washington.
To conclude, Castle Rock is a place on the island which represents control, power, and the final descent into savagery. Castle Rock gives Jack Merridew the power and control over the other boys in his tribe that he craves.